This invention pertains to color laser imaging methods and apparatus and, in particular, to methods and apparatus for detecting a low toner condition in color laser imaging devices.
Color printing by an electrophotographic printer is achieved by first scanning a digitized image onto a photoconductor. Typically, the scanning is performed with diodes which pulse a beam of energy onto the photoconductor. The diodes can be, for example, laser diodes or light emitting diodes (LEDs). The photoconductor typically comprises a movable surface coated with a photoconductive material capable of retaining localized electrical charges. In many cases, the movable surface is in the form of a revolvable cylindrical drum.
The surface of the photoconductor is divided into relatively small units called pixels. The photoconductor is generally configured to continuously revolve such that any given pixel is repeatedly moved past the diodes at a substantially regular cycle and at a substantially constant rate, and along a substantially fixed path relative to the diodes. Each pixel is capable of being charged to a given electrical potential, independent of the electrical charge of each surrounding pixel.
During operation of the printer, substantially all of the pixels are first charged to a base electrical charge as they move past a charging unit during each revolution of the photoconductor. Then, as the pixels move past a diode, a beam of energy, such as a laser, is either directed at, or not directed at, each of the pixels as dictated by the digital data used to pulse the laser. If the laser is directed at a given pixel, the given pixel can be electrically altered by changing (typically discharging) the base electrical charge to a second electrical charge.
Thus, after passing a laser during operation of the printer, a first portion of the pixels will remain at the base electrical charge because they were not exposed to the laser, while a second portion will have a different charge because of being altered by the laser. The first and second portions of unaltered and altered pixels thus form an image on the photoconductor. One portion of pixels will attract toner, while the other portion will not, depending on various factors such as the electrical potential of the toner. That is, the unaltered pixels will either attract or not attract toner, and vice versa with regard to the altered pixels.
In most electrophotographic printing processes, the altered, or electrically discharged, pixels attract toner onto the photoconductor. In this manner, toner is selectively transferred to the image made up of electrically discharged pixels on the photoconductor. This process is known as discharge area development (DAD). However, in some electrophotographic printing processes toner is attracted to the un-discharged (i.e., charged) pixels on the photoconductor. This latter type of electrophotographic printing is known as charge-area-development (CAD). The present invention is meant to encompass both DAD and CAD printers.
Once the toner has been applied to the photoconductor to form an image, the image is ultimately transferred to finished product medium, such as a sheet of paper. Although the finished product medium typically comprises paper, it can also comprise other materials such as plastic, as in the case of a transparency. Also, finished product medium can comprise individual sheets, such as a typical eight-and-one-half inch by eleven inch sheet of paper, or it can also comprise a long, continuous sheet.
The transfer of toner from the photoconductor to the finished product medium can be direct, or it can be indirect using an intermediate transfer device. That is, in the direct method, the toner is transferred directly from the photoconductor to the finished product medium. In the indirect method, the toner is transferred first to an intermediate transfer device, then transferred from the intermediate transfer device to the finished product medium. The intermediate transfer device typically comprises a revolvable endless belt. During operation of the printer, the intermediate transfer device typically moves by circulating, or revolving, past the photoconductor. The finished product medium, in turn, is caused to pass by the intermediate transfer device.
After the toner is transferred to the finished product medium, it is processed to fix the toner thereto. This last step is normally accomplished by thermally heating the toner to fuse it to the finished product medium, or applying pressure to the toner on the finished product medium. Any residual toner on the photoconductor and/or the intermediate transfer device is then removed by a cleaning station, which can comprise either or both mechanical and electrical means for removing the residual toner.
A variety of methods are known for selectively attracting toner to a photoconductor. Generally, each toner has a known electrical potential affinity. As described above, selected pixels of the photoconductor can be exposed by a laser from a base potential to a given potential associated with the selected toner, and then the toner can be presented to the photoconductor so that the toner is attracted only to the selectively exposed pixels. This latter step is known as developing the photoconductor.
In some processes, after the photoconductor is developed by a first toner, the photoconductor is then recharged to the base potential and subsequently exposed and developed by a second toner. In other processes, the photoconductor is not recharged to the base potential after being exposed and developed by a selected toner. In yet another process, the photoconductor is exposed and developed by a plurality of toners, then recharged, and then exposed and developed by another toner. In certain processes, individual photoconductors are individually developed with a dedicated color, and then the toner is transferred from the various photoconductors to a transfer medium which then transfers the toner to the finished product medium. The selection of the charge-expose-develop process depends on a number of variables, such as the type of toner used and the ultimate quality of the image desired.
Image data for an electrophotographic printer (which will also be known herein as a xe2x80x9cprinterxe2x80x9d), including color laser printers, is digital data which is stored in computer memory. The data is stored in a matrix or xe2x80x9crasterxe2x80x9d which identifies the location and color of each pixel which comprises an overall image. The raster image data can be obtained by scanning an original analog document and digitizing the image into raster data, or by reading an already digitized image file. The former method is more common to photocopiers, while the latter method is more common to printing computer files using a printer. Accordingly, the invention described below is applicable to either photocopiers or printers.
Recent technology has removed the distinction between photocopiers and printers such that a single printing apparatus can be used either as a copier, a printer for computer files, or a facsimile machine. In any event, the image to be printed onto finished product media is provided to the printer as digital image data. The digital image data is then used to pulse the beam of a laser in the manner described above so that the image can be reproduced by the electrophotographic printing apparatus. Accordingly, the expression xe2x80x9cprinterxe2x80x9d as used herein should not be considered as limited to a device for printing a file from a computer, but should also include any device capable of printing a digitized image in the general manner described herein, regardless of the source of the image.
The image data file is essentially organized into a two dimensional matrix within the raster. The image is digitized into a number of lines. Each line comprises a number of discrete points. Each of the points corresponds to a pixel on the photoconductor. Each point is assigned a binary value relating information pertaining to its color and potentially other attributes, such as density. The matrix of points makes up the resultant digitally stored image. The digital image is stored in computer readable memory as a raster image. That is, the image is cataloged by line, and each line is cataloged by each point in the line. A computer processor reads the raster image data line-by-line, and actuates the laser to selectively expose a given pixel based on the presence or absence of coloration, and the degree of coloration for the pixel.
The method of transferring the digital raster data to the photoconductor via a laser, lasers, or LEDs, is known as the image scanning process, or the scanning process. The scanning process is performed by a scanning portion, or scanning section, of the electrophotographic printer. The process of attracting toner to the photoconductor is known as the developing process. The developing process is accomplished by the developer section of the printer. Image quality is dependent on both of these processes. Image quality is thus dependent on both the scanning section of the printer, which transfers the raster data image to the photoconductor, as well as the developer section of the printer, which manages the transfer of the toner to the photoconductor.
In the case of a typical multi-color laser printer, at least one laser scanner is included and utilized to generate a latent electrostatic image on the photoconductor. Generally, one latent electrostatic image is generated for each color plane to be printed. A xe2x80x9ccolor planexe2x80x9d generally refers to a portion of the output image which comprises only a single color of toner. For example, in a four-color laser printer, the final output image comprises four color planes. This allows for each of four colors to be imaged first onto a photoconductor, then transferred onto an intermediate transfer device, and finally transferred from the intermediate transfer device to the finished product medium.
In a typical scanning process, a laser is scanned from one edge of the photoconductor to the opposite edge while being selectively pulsed in accordance with the image data file. That is, the laser scans across the photoconductor, following a row of pixels. As the laser scans along the row of pixels, it is selectively pulsed a pixel-by-pixel basis. That is, for each pixel in a row, the laser is either directed at the pixel, or not directed at it. The scan of the laser in this manner causes a line of point which make up the digital image to be transferred from the raster onto the photoconductor. As the photoconductor moves past the laser, the laser advances to the next row of pixels, and the next line of points from the digital image is scanned by the laser onto the photoconductor. The image data is thus scanned onto the photoconductor in a pixel-by-pixel and line-by-line basis until the complete image is transferred to the photoconductor.
The side-to-side scanning action of each laser is traditionally accomplished using a dedicated multi-faceted rotating polygonal mirror at which a stationary laser is aimed. The rotation or the mirror causes the reflected laser beam to be scanned across the photoconductor at a unique relative lineal position from a first edge to a second edge of the photoconductor. As the mirror rotates to an edge of the polygon between facets, the reflected laser reaches the edge of the photoconductor. When the laser is reflected off of the next facet as it rotates into position, the laser is essentially reset to the first edge of the photoconductor to begin scanning a new line onto the advancing photoconductor.
Generally, there are two types of color laser printers. One type is the multi-pass printer and the other type is the in-line printer. The multi-pass type of laser printer, also known as the four-pass, is generally provided with a single photoconductor and a single laser/mirror scanner system. The four-pass type is also generally provided with a movable intermediate transfer device, commonly in the form of an endless belt which circulates, or revolves, past the photoconductor. In operation, each of the four color planes (typically black, yellow, cyan, and magenta) which make up an output image is consecutively developed on the photoconductor and completely deposited on the intermediate transfer device. That is, as a first color plane is developed on the photoconductor, it is deposited in its entirety, as toner, on the intermediate transfer device as the device makes a complete first revolution, past the photoconductor.
The intermediate transfer device then begins a second revolution past the photoconductor during which the second color plane is developed on the photoconductor and deposited in its entirety on the intermediate transfer device in registered alignment with the first color plane. This process is repeated in like manner for the third and fourth color planes until all four color planes have been deposited on the intermediate transfer device so as to build-up the completed image thereon. It is important that each succeeding color plane is deposited exactly xe2x80x9con top ofxe2x80x9d the previous color plane. That is, each succeeding color plane is superimposed, or deposited in registration with, the previous color plane. After the image has been completed with all four color planes on the intermediate transfer device, the image is then transferred to a sheet of finished product medium.
As mentioned above, another type of printer is the in-line type. The in-line type of printer generally has a photoconductor and a laser/mirror scanner system of each color of toner. Thus, a typical in-line printer will include four photoconductors and four laser/mirror scanner systems, wherein each of the laser/mirror scanner systems correspond to one each of the photoconductors. The photoconductors are usually situated xe2x80x9cin-linexe2x80x9d relative to one another, and proximate to the intermediate transfer device. Each of the photoconductor-laser/scanner combinations is dedicated to producing a given color plane. For example, a particular photoconductor-laser/scanner combination can produce only yellow color planes, while another photoconductor-laser/scanner combination can produce only magenta color planes.
In general, multi-color printers are configured as four-color printers. However, at least three colors of toner are generally provided in order to produce at least the basic hues of the visible color spectrum. These three colors usually include yellow, cyan, and magenta. These three colors are known as xe2x80x9ccomplimentaryxe2x80x9d colors or xe2x80x9csubtractive primaryxe2x80x9d colors. The complimentary colors are known as such because they each compliment one of the primary colors which are red, blue, and green. That is, yellow compliments blue, cyan compliments red, and magenta compliments green.
The term xe2x80x9ccomplimentxe2x80x9d in this context means that light of one of the primary colors added to light of its complimentary color will yield white light. The reason for this is that light having a complimentary color is made up of light of two primary colors. That is, yellow light is made up of green light and red light. Cyan light is made up of green light and blue light. Magenta light is made up of blue light and red light. When light of each of the primary colors is mixed, white light results. Thus, when light of a primary color and light of its compliment are mixed, white light is produced since a primary color and its compliment together always comprise all three primary colors.
One reason for using toners of the complimentary colors in printing processes rather than using toners of the primary colors stems from the xe2x80x9cfilteringxe2x80x9d effect of toners. That is, toner does not produce or transmit light, but only reflects or filters light. For example, when white light is directed at cyan toner, it will act as a filter to filter out red light. That is, cyan toner will only allow blue and green light to pass through it, or be reflected from it. In other words, cyan toner removes or absorbs red light from white light, letting blue and green light pass through, or be reflected as the case may be. Similarly, magenta toner filters out green light and yellow toner filters out blue light. On the other hand, if toner of a primary color is used, it will filter out all other colors except its color. For example, red toner will filter out both blue and green light. Similarly, green toner will filter out both blue and red light, and blue toner will filter out both red and green light.
Thus, if toners or primary colors (red, blue, green) are used to create a printed image, only those three primary colors can be produced in a printed image. This is because toners of primary colors generally cannot be combined to produce other printed colors. That is, if one primary color toner is applied over another primary color toner to produce a printed image, no light will be reflected or allowed to pass through and the printed image will appear black or dark brown. For example, if a blue toner is applied over a red toner, substantially no light will be reflected or allowed to pass through the image since the blue toner will block red light and green light, and the red toner will block blue light and green light. In that case, all three primary color will be blocked and substantially all light will be absorbed. A like result is achieved in combining blue toner with green toner and in combining red toner and green toner. Toners of primary colors will be visible only if each is printed alone. Thus, if only toners of primary colors are used, images comprising only red, green and blue can be produced.
However, if toners of the complimentary colors are used, a different result is achieved. Because complimentary colors block, or absorb, only one primary color rather than two, a combination of two toners of complimentary colors will result in one of the primary colors. For example, if cyan and yellow toner are printed over one another, a green color can be produced. This is because, cyan toner will block only red light, letting green and blue light pass or reflect, while yellow toner will block only blue light, letting red light and green light pass or reflect. Thus, neither the cyan toner nor the yellow toner will block or absorb green light, which will be allowed to reflect or pass through. Similar results can be achieved in combining the other complimentary colors.
Therefore, when toners of the complimentary colors are used, both complimentary and primary colors can be produced because the complimentary colors can be printed alone, or combined to produce primary colors. In addition, varying shades can be produced by using differing proportions of each of the complimentary toner colors. In this manner, toners of the complimentary colors can be combined in printing processes to produce a fuller gamut of colors than if only toners of the primary colors were used. In addition to toners of yellow, cyan, and magenta, a fourth toner, that of black, is also generally included in multi-color printers. Although black is arguably not a xe2x80x9ccolor,xe2x80x9d it is generally referred to as one of the four colors when used in a typical four-color printer.
Toner, as used in laser printers, is generally in the form of a fine powder. Each color of toner is contained in a dedicated compartment to avoid mixing the different color toners prior to deposition of the toners on the photoconductor. The toner compartments are usually configured as cartridges which are removable from the printer apparatus. The removable nature of the cartridges facilitates resupply of the toner. That is, when the level of toner in a given toner cartridge becomes low, or when the cartridge becomes empty, the cartridge can be removed from the printer and replaced by another like cartridge which contains a supply of the same color toner.
When a low level of a given toner occurs, a result is that the given toner generally is not applied to the photoconductor in an amount in which it was intended to be applied. That is, because of the low level of toner in the toner cartridge, less than the proper amount of toner is applied to the photoconductor. This condition is sometimes referred to as toner xe2x80x9cfadexe2x80x9d since the appearance on finished product medium, such as white paper, is that of a faded color. The xe2x80x9cfadingxe2x80x9d appearance is generally due to the whiteness of the paper appearing through areas of relatively thinly applied toner. Toner fade which is due to a low toner condition is undesirable because it often results in output images of unacceptable quality.
Prior art printers often have unreliable means of detecting or anticipating a low toner condition. Thus, with regard to prior art printers, a low toner condition can go undetected until an operator or user of the printer discovers toner fade in output images which have been produced by the printer. Because a user or operator of a prior art printer typically does not continually monitor the output images as they are produced by a prior art printer, a low toner condition can go undetected, for example, during large printing jobs. This can result in a considerable number of output images which are unacceptable in quality. This, in turn, can create a large amount of wasted resources because the print job then must be redone.
One attempt at increasing the reliability of low toner detection means in prior art printers has been to include a scanner device through which the output images from the printer are passed. The scanner device digitally scans each output image, and then attempts to match the scanned image with the ideal reference image which corresponds to each output image. If any discrepancies between the scanned image and the ideal reference image are detected by the scanning process, the operator can then be alerted to the possibility of a low toner condition. However, scanner devices are known to be relatively complex, and adding such a scanner operation to the printer operation can tend to add considerable complexity to the printing process. In addition, the scanning and matching procedure, as described above, can tend to slow or limit the speed of output image production.
What is needed, then is a relatively simple and quick method and apparatus to detect a low toner condition in a color printing apparatus.
The invention includes methods and apparatus for examining toner areas in a color laser printer in order to detect a low toner condition.
In accordance with a first embodiment of the present invention, an apparatus for examining toner areas in order to detect a low toner condition is disclosed. The apparatus has at least one energy detector, each of which can be a densitometer. The apparatus in accordance with the first embodiment of the invention can also have a support surface which can be movable and which can support and move at least one toner area. As the at least one toner area is moved by the support surface past the at least one energy detector, the at least one energy detector can detect electromagnetic energy which is reflected from the at least one toner area. The apparatus in accordance with the first embodiment of the invention can also include at least one energy source which can be configured to produce electromagnetic energy and direct the energy toward the support surface and the toner area. The at least one energy detector can detect a variation in intensity of energy reflected from the at least one toner area. A given variation in intensity can indicate toner fade due to a low toner condition.
In accordance with a second embodiment of the present invention, another apparatus for detecting a low toner condition is disclosed. The apparatus in accordance with the second embodiment of the present invention can also have at least one energy detector, a movable support surface configured to support at least one toner area, and at least one energy source. However, in accordance with the second embodiment of the present invention, each of the at least one energy sources can be configured to selectively produce electromagnetic energy of one of a plurality of given wavelengths within a given range of wavelengths. For example, the at least one energy source, in accordance with the second embodiment of the present invention, can be configured to produce electromagnetic energy of a first wavelength, such as a first color, and energy of a second wavelength, such as a second color, and energy of a third wavelength, such as a third color.
In accordance with a third embodiment of the present invention, yet another apparatus for detecting a low toner condition is disclosed. The apparatus in accordance with the third embodiment of the present invention can include a movable support surface which can support at least one toner area. The apparatus also includes a plurality of energy detectors which can detect intensity of electromagnetic energy which is reflected from a toner area located at substantially any position across the width of the support surface. The apparatus in accordance with the third embodiment of the present invention can also include at least one filter which can be configured to filter electromagnetic energy reflected from the at least one toner area and before the reflected energy reaches the at least one energy detector. The at least one filter can be configured to block electromagnetic energy of certain wavelengths, while allowing electromagnetic energy having other wavelengths to pass through. The at least one filter can include, for example, a color filter which can allow light of substantially a given wavelength to pass through while blocking light of other wavelengths.
In accordance with a fourth embodiment of the present invention, still another apparatus for detecting a low toner condition in a color laser printer is disclosed. In accordance with the fourth embodiment of the present invention, the apparatus can include an energy source which is configured to produce electromagnetic energy and to direct the energy into an energy-transmitting conduit, such as a fiber optic filament. The energy transmitting conduit can be configured to transmit the energy to at least one energy transmission points, from which energy can be directed toward a support surface and toward at least one toner area which can be movably supported on the support surface. The apparatus, in accordance with the fourth embodiment of the present invention comprises a full-width energy detector which can detect intensity of energy reflected from the at least one toner area.
In accordance with a fifth embodiment of the present invention, yet still another apparatus for detecting a low toner condition in a color laser printer is disclosed. The apparatus, in accordance with the fifth embodiment of the present invention, can include a plurality of energy sources, each of which can produce electromagnetic energy of a plurality of given wavelengths. For example, a first energy source can produce energy of a first wavelength, and a second energy source can produce energy of a second wavelength. Each of the energy sources can be configured to direct energy into one each of a plurality of energy-transmitting conduits which can comprise, for example, fiber optic filaments. Each of the energy-transmitting conduits can be configured to transmit energy to each of a plurality of energy transmission points, from which energy can be directed toward at least one toner area which can be supported on a movable support surface. The apparatus, in accordance with the fifth embodiment can further include a plurality of energy collectors, which can comprise, for example, an optical lense. Each energy collector can be configured to collect energy reflected from the at least one toner area and direct the collected energy to one each of a plurality of energy detectors.
In accordance with a sixth embodiment of the present invention, a method of detecting a low toner condition in a color laser printer is disclosed. The method can include detecting intensity of electromagnetic energy which is reflected from a toner area. Detecting a variation in intensity of electromagnetic energy reflected from a toner area can also be included in the method, as can comparing intensity of energy reflected from a toner area to a reference value. The method can also include detecting intensity of electromagnetic energy reflected from a first toner area, detecting intensity of electromagnetic energy reflected from a second toner area, and comparing intensity of electromagnetic energy reflected from the first toner area to intensity of electromagnetic energy reflected from the second toner area.